Are ultrasound conception dates accurate?

[tina6146]

I discovered I was pregnant unexpectedly, and went to have an ultrasound on May 23rd. Due to having wavering periods, I never really keep track, and therefore I don't know when my last period was. I can give an "estimate" but I really don't know because I never keep track. (Plus I have always been told that because of metabolic issues, and PCOS that it would be very hard for me to get pregnant).
Anyway, not exactly proud of this, but I was with 2 different men in a two week time period. One I didn't use protection with on Saturday April 7th (we have been very good friends for years, and it just happened on a night out drinking/dancing) and the other man I only went out with a few times, and when we slept together the following week (on Saturday April 14th), the condom broke. I didn't think anything of it, because I am almost 38, and this has never happened to me before.
So, my question is, when I went to have my ultrasound, the sonographer did 2 measurements for the conception date: one was 6 weeks and 3 days, and the other one (just to be sure) was 6 weeks 5 days. So, we split the difference and said 6 weeks 4 days. This would make my conception date April 7th, which is the exact night I was with the first man.
Do you think there's a big chance that the 2nd man could potentially be the father? I am hoping the first man is indeed the father, because we have been friends for years, and it would be alot easier to handle. The second man, however, I don't even speak to anymore. I would hate for it to be the second man.
Any advice on people that have gone through this? I guess I just want some confirmation that these ultrasound dates are accurate. The ultrasound tech was amazing, and I feel like she really knew what she was doing, but I just want to make sure that these results couldn't be a whole 7-8 days off.

[hbic16]

How to ask a question on here?

[AnnieBrooke]

December 20.

[Lungi88]

I was not 42 the scan also confirmed that If gave birth 29 th Aug it was 38 and not 40

[AnnieBrooke]

If you had the baby at 40 weeks on September 12 (no doctor told you that you were 42 weeks, right?) the conception date where 40 weeks = September 12 is December 20.  

[AnnieBrooke]

Hi, Lungi, second guy for definitely sure.

[Lungi88]

My edd was 29 august (38weeks) in which 40 weeks is 12 September (actual birth date of my child) first guy 05 DEC second guy 16 dec